MooksM275

Hello Everyone,

Im trying to track down an issue with the ABC and wondered if anyone had any experience with this issue.

Symptoms:
Car feels very stiff on suspension when hitting sharp bumps on the road.
When going over speed bump, rear seems to want to quickly/sharply decompress as if it is filled with too much pressure. Over speed bumps is where the rear (and front to some extent) shows how stiff it is.
Overall feels like suspension is in Sport ++++ mode
Feels great over undulating bumps
No warning symbols on Dash
Drives through turns great with no "soft suspension" and no "tuna boat ride"


ABC System:
Pump OEM new around 10k miles ago.
Fluid level perfect/level correct on off position
Filters new and fluid is clean after flush
All 4 accumulators have been changed (including new pulsation dampner)
No sagging even when left for over one month


Im leaning toward some type of issue with the pressure relief valve, but wouldnt this show up as a "over pressure" warning? Im thinking that maybe the pressure relief valve is stuck and not releasing pressure spikes above 200bar.


My stupid SDS multiplexer broke so I am waiting on a replacement, but any advice on a specific test or data I should look at to discover this issue. Im thinking to run SDS live while driving and track the pressure. Would this show if the pressure relief valve was malfunctioning? My second though is could valve block solenoid be sending too much pressure to the strut?

Im really stumped.

Cheers.

Welwynnick

Does the car actually drive level?
Does it sit at the right height?
Is the issue repeatable / demonstrable?
Can you isolate the instances, in terms of road, speed, dynamics, etc?
Are there some instances where you don't encounter the issue at all?
Did you ever try to run a rodeo?

That's enough for now, Nick

MooksM275

1. I can see that the right (passenger) side sits about a little less than half inch lower than left (drivers). But ride height seems normal other than that. I can raise and lower via the abc button and it goes to all 3 levels.

2. Issue is repeatable over every sharp bump and feels tighter on suspension than my e63 m6 I had prior to this car.

3. Road speed doesn't matter. Suspension feels overly firm over a speed bump going slow and over expansion joints on the freeway. In terms of dynamics, car drives through turns flat and consistent. Over speed bumps or going in and out of driveways, if I am going at an angle, the car rocks left to right and does not like going at an angle through a bump at slow speeds.

4. This issue is always present. Cold hot, fast slow.

5. I ran a rodeo and the test went all the way through. The pump pressure went as low as 125 bar or so, which I heard is normal. However, the rear did not go through the rodeo smoothly. When the rear would get to the bottom out location on rodeo test it would always pause and seemed to bounce slightly. I have a video somewhere and I can post it.

As far as rodeo, I need to wait to get the multiplexer back from supplier, but wondering if there are any specific tests I should carry out or sensors to pay particular attention to. Because the right side seems lower, I assume that the plunger sensor calibration was not properly carried out. Funny, mercedes repaired the abc just prior and it seems that they did not carry this out correctly to get level ride height.

Could plunger sensor calibration affect smoothness?


Thanks for the help btw. Im hoping that a resolution to this issue can help the board out. I tried searching for someone on here with a similar issue and could not find one with a resolution. For me, I have no warning lamps, and I cna hit the largest bumps (albeit with very stiff suspension), but no warning at all. Fluid levels consistent on or off and no overflowing.

Thanks

Welwynnick

ABC sounds pretty healthy, then. It's late now, but I would start thinking in terms of the conventional suspension hardware......


Nick

Jack_88

Did you check the condition of the bushings for the control arms, sway bars, links, etc? I'm not terribly familiar with Mercs specifically, but what you describe reminds me of control arm bushings going out in Audis and Chryslers.

MooksM275

I will check everything in the coming weeks. I dont think it is only bushings for one reason. The cars behavior over a diagonal dip. I have driven lots of mercs, including a very healthy cl55 abc, and over a diagonal dip the car stays level and does not rock left to right. In my car, over this type of dip, the car rocks left to right pushing me against the sides of my seat. Feels as though hydraulic suspension is very high pressure holding the struts tight and not allowing them to articulate over a bump like this.


Im thinking that possibly I have a sticky valve in a valve block but will need to run a diagnostic to make sure. I will post results as soon as I get them.

Thanks for your help.

MooksM275

So I have a question/update....


Is it normal for the car to drop when the car is shut off (engine turned off)? I know it is normal to drop over time some, but mine drops half inch all the way around when the engine is turned off after a drive.

So, I happened to notice something I never did before. Standing outside the car in front, I had my leg up against the bumper and someone was in the car turned the engine off and I felt the car lowering. Sure enough, car drops when engine shut down.

Is this leaking valve blocks issue? funny thing is that the car can be left for over one month sitting and no drop on any corner.

ItalianJoe1

Mine does that, it drops slightly when turned off. I figured it's normal, the previous CL600 did it also.

I've also noticed on mine and others, that extended idling results in random height adjustments. I first noticed it when sitting in the car running with the door open and my leg out. Every couple minutes it would adjust the height slightly, nothing major but it could be noticed.

tusabes

That's normal don't worry about it

cside

This is extremely interesting topic for me because my car has the same symptoms. Including sudden movements during long idling. First I was thinking it was because the wind but then I noticed there was no wind. Pretty uncomfortable just to accept this to be normal.

Some unbalanced movement on rear side when driving over sharp surfaces, like a fish tail effect. Rear feels pretty hard. If I drive using height adjustment in upper or middle height, it feels more calm, generally a bit better ride.

Jack_88

I think you have a bushing in the rear suspension that has gone out or something. What you describe is normal for an older Grand Cherokee but not this.

MooksM275

So after bleeding rear struts and finding that it did not change much, I had a double check closely examining rear bushings.

Found something!! rear subframe bushings, particularly fronts are worn and have spider cracks in webbing. Second, I see black marks where the round ring portion of the subframe bushings has been making contact with the frame of the vehicle. If you look at the design of our subframe bushings, you will see that this means I essentially am running with no bushing/very little isolation effect.

I will change this out and post a diy with pics for anyone that is interested and report back on outcome. I will change all 4 while I am there.

FWIW, the dont look terrible but I guess they have loosened to the point where it is resting or making contact with the frame.


Wish me luck

tusabes

Very interested in yiur DIY write up

biker349

good luck! looking forward to the write up and results.